Study: Gallbladder Function in Obese Persons During Weight Loss Diets Purpose: A pilot project to determine the effect of different degrees of calorie restriction on measures of gallbladder ( GB ) function, and to test the feasibility of these methods to determine the effect of various dietary interventions on gallstone formation, gallbladder function, and bile composition. Methods: 20 obese subjects ( BMI 34 to 45 ) were enrolled and randomized to either very-low calorie diet ( VLCD; 450 -600 kcal/d ) or a Moderately Low Calorie Diet ( MLCD; 950 - 1100 kcal/d ), with the two diets being identical in fat content ( <5 gm/d ). On each of 4 admissions to the GCRC( at baseline, 4, 12, and 24 weeks ) subjects underwent body composition analysis including hydrodensitometry and dual-X-ray absorptiometry, studies of GB function including fasting GB volumes by ultrasound and CCK stimulated GB ejection fractions, and sampling of duodenal bile. Results: 10 of the subjects ( 6 on VLCD, 4 on MLCD ) completed all 24 weeks of the protocol, and 1 subject (on VLCD) discontinued after 12 weeks. All subjects lost weight, but subjects on the VLCD lost weight at a greater rate than those on MLCD( 1.0 +/- .13 versus 0.5 +/- .12 kg/week, p < 0.01 ). 3 of these 11 developed gallstones, but there was no significant correlation between gallstone formation and rate of weight loss in this small group. When compared fasting GB volumes prior to the diet, there were significant increases in the average GB volumes during weight loss( 31.3 cm3 versus 41.8 cm3, p<0.05 ), and a statistical trend suggested that GB volumes during weight loss were greater in the subjects on VLCD than on MLCD( 47.0 cm3 vs. 33.5 cm3, p = .14 ). No change occurred in GB response to CCK during the diets, as measured by GB ejection fraction.